Slurries comprised of suspensions of solids within a liquid carrier, with or without the presence of other liquids such as waste oils, are prepared for a variety of applications that require a continuous slurry formation process. The present applicant's co-pending application Ser. No. 08/713,358 relates to an apparatus and method for the disposal of wastes by injection of wastes in slurry form into geological formations. The slurry is prepared on the surface for this application with apparatus designed to produce a generally continuous stream of slurry. Typical wastes that may be slurrified for this process include:
oily sand from petroleum industry operations, as well as waste drilling fluids and drill chips from well drilling operations and oily slop and sand and residues from tank-bottom clean-outs;
soil contaminated with toxic materials such as PCB, heavy metals, cyanide compounds, hydrocarbons, naturally-occurring radioactive wastes, etc.;
dredging wastes;
municipal sewage sludge from which the organic wastes have been largely decomposed;
waste plastics, glass, and other solid materials;
fly ash, clinker or other residue from combustion of wood, coal or municipal wastes;
flue gas desulphurization sludges as well as recaptured particulates from smoke or emission abatement processes, whether in solid or aqueous suspension form;
high solids content sludges and residues from petroleum refining, including high ash content coke, heavy oil residues and removed solids.
Typical existing slurry-making systems employ a batch processing method, wherein slurry is generated and discharged in a series of discrete batches. This approach is not desirable for generating the high volumes of slurry that is preferred for subterranean injection applications, nor does it permit an injection pump to operate on a continuous basis. The continuous production of a steady stream of slurry is important to achieve optimal pump efficiency and to minimize pump wear.
As well, apparatus for producing slurry for use in an injection process as described in co-pending application Ser. No. 08/713,358 must meet several design criteria in order to dispose of a substantial volume of wastes at a high rate:
delivering prepared slurry on a continuous basis at a surface pressure of between 6-15 Mpa;
disposition of slurry injected at a rate of between 1.5 and 2.0 m.sup.3 /min. and 1000 m.sup.3 /day;
slurry composition with a granular solids content between 15-40% and real-time waste concentration and slurry density control to maintain density between 1100 and 1500 kg/m.sup.3 ;
processing of 200-400 m.sup.3 /day of granular wastes;
ability to accept a variety of solid materials, including slop and sand.
The operating parameters of a slurry forming apparatus for use in a waste injection system require equipment capable of preparing a relatively granular, highly viscous slurry at relatively high rates and pressures and on a continuous basis. Preferably, the slurry formation apparatus for this application should provide the following features:
a) relative ease of handling of waste material;
b) screening of granular waste material on a continuous basis to remove oversize or undesirable material;
c) a real-time monitoring apparatus to monitor and record injection parameters;
d) variable speed controls linked to the monitoring apparatus to control the various slurry-forming components and maintain consistent slurry quality and delivery rate;
e) a system capable of relatively rapid set-up and disassembly;
f) slurry formation equipment capable of shearing highly viscous material to increase slurry mobility and injectivity, maintaining slurry consistency within a relatively small range, and being capable of handling relatively large amounts of waste material, in the range of at least 100 m.sup.3 /day, which when incorporated within a slurry may result in the formation of 1,500 m.sup.3 /day slurry or more.
A further requirement of an apparatus designed to process sand or other abrasive materials is that the moving parts not be exposed to excess wear. This requirement particularly affects the material transport means within the system, which are in contact with the slurry or slurry substrate. These components should minimize the use of moving parts in contact with each other that are also in contact with the slurry mixture. As well, where the system is intended to provide slurry to a waste injection system, it is desirable to provide a dual slurry outlet, in order to permit the use of dual injection pumps to reduce wear on the individual pumps and minimize maintenance downtime of the system.